1. Field of the Invention
This invention relates in general to certain new and useful improvements in overhead door operators, and more particularly, to an overhead door operator, which precludes damage to the operator in the event of improperly set limit switches.
2. Brief Description of the Prior Art
Overhead doors, such as garage doors, are widely employed in industrial, commercial and residential applications. Very frequently, the garage door is a segmented door, which is raised to an overhead position and lowered to the closed position by means of a door operator.
The overhead door is typically constructed of a plurality of vertically arranged segments and each of the segments are pivotally connected to one another so as to be capable of turning about an arcuate bend at or adjacent to the upper portion of a track supporting the door. Moreover, rollers are secured to the individual segments and moved in a trackway at each of the opposite ends of the door. In this way, a controlled opening and closing movement is achieved.
There are a large number of different ways to couple the openable and closable door to a powered unit, such as an electric motor. One of the common ways is to cause rotation of a pinion gear which is disposed in meshing engagement with a rack and which is, in turn, driven by the drive unit. Another means for driving the garage door is to use a chain located in a guides at each of the opposite sides of the garage door. Generally, where drive chains are employed, the ends of the chains are connected either to the carriage or the connecting block mounted on that carriage rather than being connected to each other in a continuous loop. As a result, a problem can arise, as hereinafter described, in the event that limits of movement of the carriage are not properly set.
Most garage door openers necessarily employ some means to release the door from the operator in order to enable manual opening in the event of a power failure. However, in all garage door openers, it is necessary to install limit switches or like limit controlling members to control the limit of movement of the door between the open and the closed positions. In the event that is the limits are not properly set, or otherwise, if the installer is not particularly careful during installation, the carriage, which connects the garage door to the drive chains, would be driven to the upper drive sprocket. The power drive unit, such as the electric motor, would attempt to force the carriage around the drive sprocket thereby damaging the sprocket or the carriage, or both.
It can be appreciated that any inadvertent driving of the carriage to the limit of the sprockets and any attempt to drive the carriage around the sprockets would result in costly damage potentially necessitating a change of the sprockets and perhaps even the installation of a new carriage. Not only is this costly, but it is also involves time consuming repair.
There has been a need for an overhead door operator in which any inadvertent driving of a carriage to, or attempting to power the carriage around, a drive sprocket is eliminated.